1. Field of the invention
The present invention relates, in general, to dielectric ceramic capacitor compositions and, more particularly, to high dielectric ceramic capacitor compositions which can be sintered at low temperatures with low temperature-dependent dielectric loss coefficients.
2. Description of the Prior Art
Ceramic compositions which comprise BaTiO.sub.3 in combination with CaZrO.sub.3 and/or CaSnO.sub.3 have been widely used as dielectrics for capacitors. The high sintering temperatures (1,200-1,400.degree. C.) for these ceramics, however, compel layer-built condensers made from these ceramics to use internal electrodes made of precious metals, such as platinum (Pt), gold (Au), palladium (Pa) and the like. Thus, in order to utilize relatively low-priced metals, such as silver (Ag) and nickel (Ni), there is a need to develop dielectric ceramic compositions which can be sintered at a temperature lower than 1,000.degree. C.
Japanese Pat. Laid-Open Publication No. 52-87700 discloses Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3 and Pb(Fe.sub.1/2 W.sub.1/2)O.sub.3 compositions, which are asserted to meet the low temperature sintering condition. Japanese Pat. Laid-Open Publication No. 53-110500 suggests a modified composition which is improved in physical properties by adding silicon (Si) and manganese (Mn) to the composition of the supra patent. The layer-built condensers employing these dielectric ceramic compositions, however, are found to be problematic in practice because the ceramic compositions are poor in temperature-dependent dielectric loss coefficient.
There have been developed Pb(B.sub.1, B.sub.2)O.sub.3 -based dielectric relaxor compositions (T. R. Shrout and A. Halliyal, "Preparation of Lead based Ferroelectric Relaxors for Capacitors", Am. Cerm. Soc. Bull., 66[4], 704 919870; M. T. Lanagan, N. Yang, D. C. Dube and S. J. Jang, "Dielectric Behavior of the Relaxor Pb[Mg.sub.1/3 Nb.sub.2/3 ]O.sub.3 Solid-Solution System in the Microwave Region", J. Am. Ceram. Soc., 72[3], 481, 83 (1989)). They can be sintered at low temperatures and show stable temperature coefficients in a range of operation temperatures with a broad range of dielectric constants. They are quite different from the present invention in technical constitution.